The mineral growth of the human fetus may be determined from the chemical composition at various stages of fetal development. Data on the chemical composition from which such growth can be shown earlier than the sixth lunar month are, to our knowledge, practically lacking in the literature. This may be due to the difficulty of obtaining sufficient material for the macrochemical methods used by the earlier investigators. In the present study, we were able, using microchemical methods, to study the chemical composition of the human fetus as early as the third lunar month.

In a series of sixteen fetuses, analyses were made for sodium, potassium, calcium, magnesium, phosphorus, chlorine and nitrogen. The analyses of the two youngest fetuses are not complete, since there was not sufficient material for all the microchemical methods. Data which give the per cent of body fat, constant dry weight and per cent of water are